BL/CH 401 Lecture #4 -- Amino Acid Structures

Aromatic NON-POLAR AMINO ACIDS

Non-Polar -- Aromatic -- Phe (Phenylalanine) -- in computers Phe = F

{*Figure 8*}

Phe adds a benzene ring to Ala!

Non-Polar -- Aromatic -- Trp (Tryptophan) -- in computers Trp = W

{*Figure 9*}

Trp has a heterocyclic aromatic group with an aromatic amine in it.

Aromatic amines (emphasized in Fig. 9) like in Trp do not ionize

since the Nitrogen has its free electrons tied up in the Pi cloud

with the electrons of the Carbon-Carbon aromatic double bonds.

Aromatic Pi clouds allow them to bond together via interaction of the Pi electrons.

The planar character of aromatic side chains helps the Pi cloud bonding.

{*Figure 9a}

Pi electrons physically lie above and below the plane of the aromatic ring.

Because of Pi electrons aromatic AAs absorb light in the UV!

©Wilbur H. Campbell, 1995, 1996; wcampbel@mtu.edu

Back To: Lecture 4 - Amino Acid Structures